This invention relates to mass transfer devices in which different fluids are exposed to opposite sides of a semi-permeable membrane so that one or more components of one fluid will pass through the membrane to the other fluid, and more particularly to embossed material for supporting the flexible membrane material in blood dialyzers for use as artificial kidneys.
Prior to the present invention, a great variety of suggestions have been published for supporting the usually thin and flexible membrane in mass transfer devices, and particularly in dialyzer devices, some of which have been exploited commercially and some of which have not. The present invention will be described in terms of a dialyzer coil for use as an artificial kidney, although it is to be understood that the invention is not limited to the same because the support material of this invention is useful in flat plate and other types of blood dialyzers as well as other types of mass transfer devices.
Dialyzer coil designs which have been exploited commercially utilize mesh or netting material made up of intersecting strands as a support for the flattened tubular membranes. Early coils such as those disclosed in Metz U.S. Pat. No. 2,880,501 issued Apr. 7, 1959, and Broman U.S. Pat. No. 2,969,150 issued Jan. 24, 1961, utilize an over-and-under woven type of mesh material. A significant improvement in commercial dialyzer coil design was brought about by the use of a particular non-woven plastic netting disclosed by Dr. Theodor Kolobow in "A New Dynamic Disposable Artificial Kidney", Transactions, American Society For Artificial Internal Organs, Volume X, pages 116-120 (1964), and Proceedings, Conference on Hemodialysis, (Nov. 9-10, 1964) National Institute of Health, Bethesda, Md., pages 87-94. The same non-woven plastic netting is disclosed as being useful in a multiple-start-spiral design of dialyzer coil in Hoeltzenbein U.S. Pat. No. Re. 27,510 issued Oct. 24, 1972, an improved orientation for the non-woven strands of such netting is disclosed in Miller U.S. Pat. No. 3,508,662 granted Apr. 28, 1970, and a particular cross-sectional shape for such strands is disclosed in Martinez U.S. Pat. No. 3,709,367 issued Jan. 9, 1973.
Membrane support material which does not make use of intersecting strands arranged in the form of a mesh or netting has also been proposed, and used to some extent commercially, although it is believed that such material has not met with any significant commercial success to date in disposable type dialyzers, particularly the popular coil types. Gobel and Bluemle U.S. Pat. No. 3,077,268 granted Feb. 12, 1963, discloses a dialyzer coil utilizing a support material comprising radially impervious plastic sheet having "hobnail" embossments protruding from the opposite sides thereof. This material is disclosed (FIGS. 1-6) as being useful in a coil design where the support material is located outside the flattened tube of membrane material so that the blood passage within the tube is relatively long and spirally directed and essentially linear in cross-section, and the passage for the dialysate is relatively short and axially directed and spiral in cross-section; and, also is suggested (FIG. 7) for use in conjunction with the known alternative coil design where the operation is reversed with an elongated sheet of support material located inside the flattened tube of membrane material. To avoid interdigitation of the peaks of the hobnail protrusions 36 which would substantially occlude the blood passage in the first design, the Gobel and Bluemle patent provides a series of large protrusions 34 and a thickened separator rim 21 having a longitudinal groove 24 on one side and cooperating disc-shaped projections 25 on the other side to prevent axial shifting of adjacent turns or wraps of the coil. To avoid interdigitation which would substantially occlude the blood passage in the second alternative design, the coil desirably is provided with end cheek plates of the type known from the aforesaid Kolobow publications to prevent axial shifting of adjacent turns or wraps of the coil. Bluemle U.S. Pat. No. 3,362,540 issued Jan. 9, 1968, discloses a membrane support for a flat plate type of dialyzer which has embossments which take the form of hexagonal based cones which are rounded at their tops, but in this device interdigitation of the opposed protrusions which would substantially occlude the blood passage is avoided as a problem during operation by the use of spacers at the edges. See also the Progress Reports of Dr. Bluemle for the period 1 November 1960 to 31 October 1961, and the period 1 November 1961 to 31 October 1962, available from the Armed Services Technical Information Agency under AD-266 -102 and AD-291-891, respectively, Esmond U.S. Pat. No. 3,695,445 issued Oct. 3, 1972, and Janneck U.S. Pat. No. 3,753,712 issued Aug. 21, 1973. In the coil and flat plate devices disclosed in these patents and publications, the embossments always are arranged in identical geometrical patterns which are not angularly off-set with respect to each other so that the embossments on one side of the blood passage are spaced apart exactly the same along any given directional line as the directly opposed embossments on the other side of the blood passage, and this creates the unacceptable possibility that the opposed embossments can interdigitate and substantially occlude the blood passage, and also the passage for dialysate, unless special spacing features are provided as aforesaid.
Thus, the problems heretofore unsolved by the prior art are the provision of membrane support, which does not make use of intersecting strands arranged in the form of either a woven mesh or a non-woven netting, consisting essentially of embossed material which positively avoids interdigitation of the embossments to an extent which would substantially occlude the blood and dialysate passages yet does so without the necessity of providing special expensive and/or cumbersome positioning or spacing features to insure against such unacceptable interdigitation.